Automatic code selector



W. W. MCGQFFKN AUTOMATIC GODE SELECTOR Filed March 2&3, 1,947

POD

Patented July 11, 1950 AUTOMATIC CODE SELECTOR William Walter McGofln,New York, N. Y., as-

signor of one-fifth to S. S. Baker, New York, N. Y.

Application March 28, 1947, Serial No. 737,905

Claims.

This invention relates to an automatic selector of Morse code signalsand more particularly to an apparatus designed to respond to aparticular combination of such signals.

An object of this invention is to provide an apparatus whichautomatically responds to a predetermined series of dot and dash signalsin such a way as to exclude any undesired combination and to performthis function in an accurate and simplified manner requiring a minimumof component parts. Thus, two relays perform four elements of timing,that is, dots, dashes, intervals and spaces, the time between the dotsor dashes of a letter being designated as intervals and the time betweenletters being designated as spaces. rlhe provision of the two timingrelays in the manner hereinafter described permits the apparatus tooperate over a wide variation of code speeds so that when the apparatusis set for a particular speed, it will respond correctly althoughreceiving code signals which depart considerably from the predeterminedspeed setting.

Another object of this invention is to provide an automatic coderesponding apparatus which re-sets itself to starting position upon` thereception of any undesired letter component, such a component comprisingeither a dot, dash, interval or space, andy wherein the apparatusremains re-set until another letter is started. Thus, a part of a letterwill not restore the apparatus to activity whereby false responses areavoided.

Another object of this invention is to provide an apparatus wherein twomechanically ganged stepper switches respectively respond to dots anddashes on the one hand, and intervals and spaces on the other hand, sothat such signal components may be swiftly and accurately recordedthereby permitting faster and simpliiied operation as well asadaptability to varied code speeds.

Still another object of this invention is to provide neutral receptionmeans whereby the letters of a signal will be accepted and a responseproduced whether or not the proper spacing between such letters isobserved. This feature is of considerable importance in S O S signalswhere the letters are often run together without including letterspaces. Under such varyingcondtions of sending, the apparatus willnevertheless respond so as to sound an alarm when an S O S signal isreceived.

A further object of this invention, as represented by a modification, isto provide an apparatus of this type which in large measureautomatically adapts itself to the code speed of reception. This isaccomplished by the use of a 55 represented by interval wire lll.

condenser element which sets the delay time of a relay so that thelength of dashes, as opposed to dots, or, of spaces as opposed tointervals, can be measured. The condenser element is arranged to carry acharge which is inuenced by the rate of code speed so that the delaytime or the relay is correspondingly iniiuenced and the signalcharacters are measured with the code speed as a factor.

This application is a continuation in part of my prior applicationSerial No. 550,862, liled October 28, 1944, now Patent Number 2,446,943.

Other objects of my invention will be apparent from the followingdescription, it being understood that the above general statements ofthe objects of my invention are intended to describe and not limit it inany manner.

Fig. l is a schematic representation of the apparatus.

Fig. 2 is a schematic view illustrating a modied form of a delayed relayaction.

The selector or stepper switch is of the dual type which, upon relayactuation, progressively wipes over a radially disposed series 0fcontacts arranged at two levels designated herein as switchesl Sl andS2'. Switches Sl and S2 have their main or relay actuated arms gangedtogether for simultaneous movement. Each series of contacts are furtherselectively connected to one of a bank of switch positions, theselection depending upon the call which the apparatus is set up torespond. Thus, switch Sl, upon which the dots and dashes are set up,includes a series of selector arms 25-29 etc. which may be set on anyone switch position of the switch banks such as bank l5. The arms 25-29etc. are normally set on the release or reset circuit i6 and when theyare switched to one of the other circuits as hereinafter set forth, theyselect the dots and dashes of the desired combination. Thus, if thefirst character of the predetermined call is a dot, the switch arm 25 isset at the first switch position of the bank l5. .lf a dash follows, thearm 2S is switched to the second switch position of bank Il.

During the operation of the apparatus, arm 3l of switch Sl successivelywipes over the contacts 3|-36 etc. each of which are selectivelyconnected to the reset, dot or dash circuits according to thepredetermined call.

The selector arms Iil-I etc. of the banks of switches of switch S2 areprogressively set at either interval or space, the normal position ofarms IBG-|05 being at the interval position as Thus, switch series S2 islikewise provided with switch bank positions although each bank inseries S2 has four positions as hereinafter set forth. The last space ofthe desired call is not set at space but the last used arm of theselector arms H-E05 etc. is set at alarm instead. It will be seen,therefore, that the call is set up by alternately proceeding from Si toS2, setting up the dot and dash characters on Si and the intervals andspaces at S2 where they occur in the call.

The dot and dash pulsations are appliedI through dash wire SS or dotwire S9 to the dot and dash interpreter circuit 22 which is identied inFig. 1 by broken lines. This enables each incoming pulsation to bechecked as to its dot or dash character and the stepper switch isadvanced or reset according to the correspondence of such character withthe predetermined and pre-set call.

Pulsing relay ll is connected to the output of an ordinary radioreceiver which is tuned to the call frequency. Thus, pulsing relay tldelivers the received signal to the apparatus for interpretation andalarm action if indicated. In the initial action, each incomingpulsation is applied to main switch arm 3l through wiret and contacts 39and l0 of pulsing relay i. If the incoming pulse coincides with theselector switch arm setting to the interpreter circuits, the arm 31 isallowed to advance through the action of the spring 42 which pulls thedog 43 against the action of the'return spring IM at thev end of thepulsationyStepper relay l5 is Yenergized by the relay il through thecontact 39 so that relay 45 receives the same potential that is appliedto arm 3l. This pulls armature 46 and drops the dog 43 into the nexttooth. Then when relay l5 is released, dog 43 pulls the toothed wheelstepper :t1 forward a notch through the action of spring ft2. vancedposition by pawl e8 whichis controlled by reset relay 63. Mechanicalarmature 46a operated by reset relay 03 and through the linkage shownsimultaneously disengages the dog 03 and the pawl 48 allowing thespringed to return to the stepper wheel lll to starting position.

Simultaneously with applying the pulsation to the relay 135, it is alsoapplied to the dot and dash timing relay 50 through the contacts 65 andRelay 50 is'of the delayed closing type accom- Yplished by the condenser5| which is effectively interposed across the relay winding when it isnot energized. The time delay includes there- Vsistors EZ-Et either oneof whichemay be switched into the circuit so as to regulate the delaytime of relay 50. In a practical embodiment, resistors 52-5il were 5000,10,000 and 15,000 ohms respectively, while condenser 5l was l0microfarads. The winding of relay 50 was of 10,000 ohms direct currentresistance. It is understood, of course,

Ithat the values of these elements will be selected according to thedelay required. This time delay permits relay 50 to closeon a pulsationwhich is of dash length but not of dot length and the length isadjustable by selecting the proper resistor. When relay 50 -does close,condenser 5l is effectively removed from the coil E50-by opening ofcontacts 200 and 201 allowing the relay to have instantaneous releaseaction. This release is eifected at the end of the pulsation because thereturn lead from lrelay 50 goes -through contact E5 ordinarily to arm 66which is connected to the negative source ofspower through'contactf l'lof reset relay 68.Y However, when relay lll releases, contact l(i5 isremoved from' the negative Stepper wheel il is maintained Ain its-ad-.which would make the delay time of coil 50 variable. In the modifiedembodiment, advantage is taken of this variation but in the instantembodiment, the condenser is substantially discharged Y at the end ofeach pulsation.

When arm 25 is set on the dot circuit, negative potential originating atelectrical line Ll is applied to stepper arm 3l at the beginning of apulsation and is immediately placed on relay arm 'i5 through the dotwire 69. Since relay 50 is fed with each pulsation through contact 65,it starts timing the pulsation but isnot allowed to close unlessy a dashis received. Therefore, if the inn coming signal is a dot and conformsto the switch Si setting, the reset is not operated and the stepper isadvanced. However, if a dash'is receivedand relay 50 allowed to`close,relay arm 'l5 which has negative potential makes contact with relay armi6 which in turn operates the stepper reset relay 60. As hereinafterexplained, this causes the stepper switch to reset to starting positionbecause the vproper sequence of call characters has not been observed.During the rst pulsation, therehas been no checking for interval orspace as the stepper arm lll has not yet advanced to the first position.It will be observed that this second level of the stepper represented'by switch S2, follows one step behind the dot and `dash level asrepresented by switch S l.

Dot and dash acceptance and rejection When selector arm 25 or any otherselector arm of switch Sl is set to the dash circuit in accordance withthe desired call, the negative potential is applied to Vand immediatelyoperates relay 82 which is energized through contact 0l and armature ofrelay A50 and locked in closing position byrelay 85. In the drawing,those terminals marked are connected directly to lead line 88 which isnormally connected to the negative source Ll through contacts |55 andI52as hereinafter described. Until the alarm is operated, line 381salways negative. The relay immediately closes on each incoming pulsationfollowing a letter space and remains closed vuntil another letter space.is received. As will hereinafter be described, relay S5, which isdelayed in-releasing, interprets, together with its .associated relaySli), intervalA and space signal components and `provides anelectri-callock on relay through contacts 83 and 84.v

- Simultaneously with the operation of relay 82, the negative potentialplaced on the dash circuit wire 89, is applied through armature 9i andcon- Relay ill being thus far closed, no potential gets to resetrelayli. If the incoming pulsation is a dash sol that sufcient time isgiven relay 50 to close, contacts B and 8i are opened, which opens thegroundcircuit of relay 82releasing it notwithstanding thepreviouslocking effect secured by armature and vcontact v96 through the contacts83 and 84. However, if a dot is received and contacts 80 and lStare-notopened, relay 82 remains locked in 'through contacts 95 and 36l andcontacts 83 and B4. Sinceafter the beginning of the pulsation,

negative potential was placed through contacts 9|-, 92 to contact` 93,the reset 68 is operated at the end of a dot pulsation when the armature9'1 returns to normal position. This shows that at the beginning of apulsation when SI. is on the dash circuit, relay 82 isimmediately-closed and negative potential placed on contact 93 throughcontacts 9i and 92 so that if only a dot is received, the reset will beoperated when armature Sl makes contact with $3 at the end of the dotpulsation. Since the negative potential supplied relay 32 is broken atthe end of the dot pulsation, it is necessary to have an electrical lockon relay 82 through contacts 95 and 96 and through contacts 83 and 84 inorderto maintain negative potential on s3. Thisy negative potential willremain on 93 until a dash is received so that anything else than a dashwill operate reset relay 68 and return the selector or stepper switch tostarting position. When, however, a dash is received suicient to closerelay 5?, contacts 8D and 8l are opened so that relay 82 releasesremoving the negative potential from contact 93., Hence, it can be seenthat if the pulsation is of suiiicient length to constitute a dash,subsequent opening of relay 4I will not operate the resetting relay ES.The stepper, however, is operated at the end of the pulsation ashereinabove stated. The acceptance or rejection of dot characterpulsations follows the explanation hereinabove set forth. Thus, witheach advance of the stepper, the next pulsation is checked to seewhether it corresponds to the original setting of the selector switcharms.

Interval and space acceptance and rejection Relay 4I supplies thepotential of the incoming pulsations not only to the dot and dash relaysbut simultaneously to the interval and space relays contained in theinterval and space interpreter circuits S8. Switches SI and S2respectively represent a series of switches which are mounted on acommon support. Switch arms 'I1 and 3l are ganged for simultaneousmovement so that as arm 3l advances, arm 'l'I similarly advances alongthe successive switch contacts wil-|35 etc. Switch arm I7 is directlyconnected to the negative lead Li so that it has negative potential onit at all times. It will be observed that the initial position of switcharm Tl is at contact Hill which is not connected to any circuit inasmuchas spaces and intervals are checked only after the rst letter component,i. e. either a dot or dash, has been received so as to advance switcharm 'll to the switch contact Illl. At this point, timing for spaces andintervals commences. Assuming now that switch contact lill is on aninterval circuit as illustrated in Fig. 1, negative potential is placedon contact IBS which is not engaged with armature I0? as relay 85, dueto its delayed action is still closed for a period of time not exceedinginterval time. Ii a space is made allowing relay 85 to release, armatureIill engages contact Iti completing the circuit to reset relay 68bringing the selector relay to starting position by its spring returndit. Thus, it can be seen that if the selector switch S2 is placed atinterval and a space sufficient to release relay 85 is received, theapparatus will reset and reject the call. lf the interval was not ofsufficient duration to cause contacts IDS and lol to engage, then thenext pulsation would maintain relay 85 energized through contact 8S sothat reset potential would not get to the relay 63. When S2 is set tothe space circuit, negative potential. is immediately placed on armaturel Ii) which is not engaged with contact Ell because of the delayedrelease time of relay 535. Negative potential is, however, placed oncontact Il2 and through armature IIS to contact IIll. Contact I I4 doesnot engage armature @l until the beginning of the next pulsation. If aspace is not received, however, when the switch arm is set for space, asset forth, then relay S5 is not given suilicient time to drop out beforethe beginning of the next pulsation. It will be recalled that relay 90is associated with relay S6, such relay SE is energized only when relay85 is released. Therefore, contacts II2 and I iii are engaged andnegative potential from the space circuit is on contact Il4 so that atthe beginning of the next pulsation, armature 'l applies the potentialto reset relay 68.

Ii, however, a space is made allowing relay c5 to drop out, engagingcontacts Il@ and III, relay 9U is operated removing the negativepotential from contact Iiil by opening the circuit at Il and H3. Thus,when a space is made when the switch is set for a space, there will beno rejection and the stepper arms will advance another step. It will benoted that when relay closes, it will electrically lock itself throughcontacts IE5 and IIi through arm II'I and contact H3 of relay iii. Atthe beginning of the next pulsation it is evident that engagementbetween contacts l iii and I I I would be broken by the operation ofrelay 5:5. This would release relay 9G which would operate the resetthrough the contacts ll2 and i it through the armature Ill and contact Iit. it is necessary, however, that this is not effected and,accordingly, relay QG is locked so as to remain energized through itscontact H5 and armature IIG which receives negative potential from thearmature l il and contact lill. At the end of the pulsation, whenarmature lil' returns to normal position, the lock is broken, arm ll'advances to the next circuit position and timing procedure repeats forthe next position.

It will be noted that the provision of switches SI and S2 as described,makes speciic wiring for a predetermined call unnecessary because theindividual switch arms can be set as required for practically anycondition. In the bank or switches of selector S2, each switch bank offour terminals has a neutral terminal which precedes the other switchpositions. When a baril; switch arm is on the neutral position, any timebetween pulsations will be accepted whether it is en interval -or aspace. It will be appreciated that the flexibility of the apparatus isconsiderably enhanced thereby. Two advantages of the neutral positionare the following:

l. In S O S signals, the letters very often run together without regardto intervening spaces. Automatic transmitters of S O S signals usuallyrun the letters thus together. Ii the `apparatus were set to receive aspace between the letters, a rejection would be ei'iected and theapparatus `would not respond. However, using the neutral positionbetween letters and intervals etween the letter components, the S 0 Swill come through whether or not the letters are duly separated. It willfurther be observed that the event a space is received during part ci aletter, it will be rejected because the switch is at the intervalsetting.

2. Experienced radio operators of code transmission often run letterstogether which cannot possibly form a false letter. Thus, A and N yarenever run together becausD tb ey would form Reset operation As thereception of the switch arms progresses, switch larms 3l and ll advanceso as to wipe over the selector switch contacts. As hereinabove stated,if any improper letter component is received,A the spring 44| returnsthe toothed wheel and its switch arms to the home or initial position.The operation of the reset relay 68, which through its mechanical actionaccomplishes this, also carries electrical contact armatures |25 and |26and contacts |21 and |28. Upon operation of the reset relay, armature|25 is disconnected from contact |21 which removes the negativepotential from armature d and 66, thereby stopping all further operationof stepper relay 45 and timing relay U. This results because negativepotential Awhich is on armature 40 from contact |21 ordinarily suppliesclosing potential for relay 56 as well as relay B5. However, after arelease or reset has been effected, it is necessary to disable theapparatus until a space is received. Otherwise, the apparatus mightreject part of a letter and then proceed on the next part as if thatnext part were a complete letter in itself. By requiring a space to beobserved after each rejection, whole letter operation is assured. Thedisabling of the apparatus until a space is received is accomplished bymeans of the electrical lock on relay 68 through contacts |30, |3| ofrelay 85 which is itself slow to release and will not drop out until aletter space is made. Thus, when a rejection is made, all circuits savethe relay 85 are disabled and the release of relay 85 starts the actionagain. This is accomplished by relay 68, contact |28 and armature |26,which provides an electrical lock on the reset relay `63 througharmature |36 and contact |3| of relay 85. It will be remembered thatrelay 85 is maintained energized by means of the incoming pulsationthrough contact 86 and arm '31. When a sufficient letter space is madeallowing relay 85 to release, armature |36 leaves contact |3| openingthe electrical lock on relay 68 which also restores Iarmature |25 tocontact with |27 which restores negative potential to armature lill.Thus, the next letter is ready to be checked since all circuits are inoperation.

Alarm When the proper signal for which the apparatus is set up isreceived, the alarm bell |50 is sounded so as to provide an audibleindication of the reception of a call. This is accomplished in thefollowing manner:

Originally, when setting up the call on the selector switches, the lastswitch representing a letter space is set at the alarm contact insteadof a space. This means that after the switch arms have progressedthrough the call, switch arm l1 with its negative potential Iwill beeffectively applied to the alarm circuit, as represented by the switchcontact |04 of the Switch S2 according to the set-up in Fis. 1..Negative potential is applied to relay |5| through contacts |69 and |6|when relay falls out with the last letter space so as to attract thearmatures |52 and |53 of relay |5|. Negative potential from lead L| isthereby applied through armature |53 to contact |54 so as to operate thebell |56. Simultaneously, attraction of armature |52 disconnects thenegative potential from contact |55 which cuts off any further currentto the apparatus. This stops all operation of the apparatus except forthe relay |5| which is connected to the negative lead L| throughselector switch arm 'Vl connected thereto. This connection is not shownon the drawing for purposes of clarity. The bell |50 lwill then continueto ring until manually operated reset switch |56 is closed. Manualoperation of this switch applies the negative potential to reset relay66 which thereupon closes and resets the stepper the same as resets aremade by rejections. This returns arm ll to switch Contact lill) so as toremove the negative potential from the alarm circuit whereupon relay |5|is released and the bell stops ringing.

It Will be understood that the last letter must not be followed by a dotor dash as otherwise it would constitute a different letter for whichthe apparatus was not set. Therefore means are provided to reset theswitches if a letter space is not made when arm 'il engages the alarmcircuit and another dot or dash is added to the last character insteadof a space. This is accomplished by setting the selector switchfollowing the last dot or dash setting to the reset circuit which goesdirectly to relay 68. Thus, if another dot or dash is applied throughthe switch arm it will energize relay 68 so as to reset the stepperswitches. In this event, no alarm will be sounded.

It will be recalled that resistors 525| are selected in order that theclosing time of relay 56 may be predetermined depending upon Whetherfaster or slower speeds are to be accommodated. In the same manner, theinterval interpreter circuit as represented by relay 65 is provided Withtiming condensers H5, ll and lll in order that the delay time oi' relay'd5 may be adjusted. This is for the purpose of presetting the apparatusin accordance with the expected speed or" reception. lt is, of course,understood that the apparatus Will operate satisfactorily over aconsiderable ldeviation trom a predetermined setting. This is madepossible by the delayed closing and releasing relays which start timingall pulsations as dots until they extend to dash length. In other words,a dot may be any length, however short, until it extends to dash lengthwhereupon it is, of course, considered a dash, and a dash may be oi'-any length as long as it exceeds the dash time which is set by theresistors til-5s. Similarly, the interval time may be as long as desireduntil it becomes space time. This provides extremely wide variation incode speed reception since dashes are normally three times as long asintervals. The time delay relays are set to operate at va timing pointone-third the normal dash length 'and one-third of' the letter spacetime so that a signal component which does not effect operation of thetwo timing relays is a dot or an interval respectively.

In a modified embodiment, I have devised means to render the apparatussubstantially automatically responsive to the desired signalirrespective of any settings of relays in anticipation of code speedconditions. This is accomplished by selecting a value of resistor l2which will delay the leakage time of the condenser 5|. Ordinarily,resistor l2 may be o l a value of 500 ohms, While 9 condenser is 10 mid.However, by increasing resistor 'l2 to a much higher value, i. e.approximately 500i) ohms, the discharging of the condenser 5i isdetermined by the operating speed of the pulsing relay il which effectscontinuous making and breaking ci the contacts 'I0 and If the operationis very fast, the condenser charge will not have an opportunity to leakofi between pulsations and a partial charge will always remain thereondecreasing the delay time and increasing the closing speed of the relay5i] to conform with the speed of the incoming signals. This action willrender the dot and dash interpreter circuits automatically adaptable tovarying speeds. It is also necessary to similarly control the space andinterval time. Referring to Fig. 2, the required modification of thedelayed release relay 85 is illustrated. The feature of adaptability isaccomplished by inserting resistor |35 in series with condenser |85across the relay winding so that the condenser is not immediately fullycharged. In addition, contacts |81 and |88 are provided to short outresistor |35 when piusing relay 4| is released allows condenser |86 tohold relay 85 closed for the duration of time in proportion to thecharge received through resistor |85 while relay il is closed. If theoperation of relay 4| is fast, condenser |86 is correspondingly chargedto a lesser degree which allows relay 85 to drop out more rapidly atsignal interruptions, the term interruptions referring to eitherintervals or spaces.

While there has been described what at present is considered a preferredembodiment of the invention, it will be evident that many changes andmodifications may be made therein without departing from its spirit. Itis therefore aimed in the appended claims to cover all such changes andmodifications which fall within the true spirit and scope of theinvention.

I claim:

l. In a signalling system for identifying a transmission of Morse codeletter pulsations constituting a desired call, the combination of analarm, electrical circuit means to operate said alarm, a selector deviceoperating to progress in steps from a starting position to a positionwhere it closes said electrical circuit means when a completepredetermined transmission has been received, release relay means forreturning said selector device to said starting position when anundesired call is received, said selector device comprising a firstseries oi switch elements for preselecting the desired dot and dashcharacters, a second series of switch elements for pre-selecting thespace and interval interruptions and switch arm means for progressingalong the respective series of switch elements as the proper pulsationsfrom said transmission are applied to said system, a slow closing relayenergized by said pulsations and operative to close when a pulsation ofdash length is received, said release relay means being operated by saidslow closing relay through said first series of switch elementsaccording to the preselection o said dot and dash characters thereon, aslow releasing relay energized at each received pulsaticn and operativeto open at a signal interruption of space length, said release relaymeans being operated by said slow releasing relay through said secondseries of switch elements according to the preselection of said spaceand interval interruptions thereon, nonmoperation of said slow closingand slow releasing relays respectively determining the dot and intervalnatures of a received pulsation, and said second series of switchelements including a neutral position by which its switch elementsremain unconnected to either space or interval positions so as toprevent operation of said release relay means through said second seriesof switch elements.

2. In a signalling system for identifying a transmission of Morse codeletter pulsations constituting a desired call, the combination of analarm, electrical circuit means to operate said alarm, a'selector deviceoperating to progress in steps from a starting position to a positionwhere it closes said electrical circuit means when a completepredetermined transmission has been received, release relay means forreturning said selector device to said starting position when anundesired call is received, said selector device coinprising a firstseries of switch elements for preselecting the desired dot and dashcharacters, a second series of switch elements for pre-selecting thespace and interval interruptions and switch arm means for progressingalong the respective series of switch elements as the proper pulsationsfrom said transmission are applied to said system, a slow closing relayenergized by said pulsations and operative to close when a pulsation ofdash length is received, said release relay means being operated by saidslow closing relay through said first series of switch elementsaccording to the preselection or" said dot and dash characters thereon,a slow releasing relay energized at each received pulsation andoperative to open at a signal interruption of space length, said releaserelay rneans being operated by said slow releasing relay through saidsecond series of switch elements according to the preselection of saidspace and interval interruptions thereon, non-operation of said slowclosing and slow releasing relays respectively determining the dot andinterval natures of a received pulsation, said selector device includingan actuating relay, said actuating relay being directly fed by saidpulsations, a pair of contacts on said actuating relay, said pair ofcontacts being electrically interposed between said rst series of switchelements and said slow closing relay and being normally closed, saidpair of contacts energizing said release relay when a dot is receivedwhen said first series of switch elements is set for dash operation.

3. Apparatus according to claim 2 and including a second pair ofcontacts on said actuating relay, said second pair of contacts beinginterposed between said iirst series of switch elements and said slowreleasing relay and being normally open, said second pair of contactsenergizing said release relay when an interval occurs when said firstseries of switch elements is set for space operation.

4. In a signalling system for identifying a transmission of Morse codeletter pulsations constituting a desired call, the combination of analarm, electrical circuit means to operate said alarm, a selector deviceoperating to progress in steps from a starting position to a positionwhere it closes electrical circuit means when a complete predeterminedtransmission has been received, release relay means for returning saidselector device to said starting position when an undesired call isreceived, said selector device comprising a irst series of switchelements for pre-selecting the desired dot and dash characters, a secondseries of switch elements for pre-selecting the space and intervalinterruptions and switch arm means for progressing along the respectiveseries of switch elements as the proper pulsations from saidtransmission are applied to said system, a

slow closing relay energized by said pulsations and operative to closewhen a pulsation of dash length is received,lsaid release relay meansbeing operated by said slow closing relay through said rst series ofswitch elements according to the preselection of said dot and dashcharacters thereon, a slow releasing relay energized at each receivedpulsation and operative to open at a signal interruption of spacelength, said release relay means being operated by said slow releasingrelay through said second series of switch elements according to thepreselection of said space and interval interruptions thereon,non-operation of said slow closing and slow releasing relaysrespectively determining the dot and interval natures of a receivedpulsation, a condenser and resistor in the circuit of said slow closingrelay for regulating its closing time, said slow closing relay includinga normally closed pair of contacts connecting said condenser to thewinding of said slow closing relay, operation of said slow closing relayopening said contacts so as to remove the condenser from the relaycircuit and permit instantaneous release thereof.

5. In a signalling system for identifying a transmission of Morse codeletter pulsations constituting a desired call, the combination of analarm, electrical circuit means to operate said alarm, a selector deviceoperating to progress in steps from a starting position to a positionwhere it closes said electrical circuit means when a completepredetermined transmission has been received, release relay means forreturning said selector device to said starting position when anundesired call is received, said selector device comprising a firstseries of switch elements for preselecting the desired dot and dashcharacters, a second series of switch elements for preselecting thespace and interval interruptions and switch arm means for progressingalong the respective series of switch elements as the proper pulsationsfrom said transmission are yapplied to said system,

a slow closing relay energized by said pulsations and operative to closewhen a pulsation of dash length is received, said release relay meansbeing operated by said slow closing relay through said rst series ofswitch elements according to the preselection of said dot and dashcharacters thereon, a slow releasing relay energized at each receivedpulsation and operative to open at a signal interruption of spacelength, said release relay means being operated by said slow releasingrelay through said second series of switch elements according to thepreselection of said space and interval interruptions thereon,non-operation of said slow closing and slow releasing relaysrespectively determining the dot and interval natures of a receivedpulsation, condensers in the circuits of said slow closing and slowreleasing relays for determining the time constants of said slow closingand Slow releasing relays and means to feed said condensers by incomingpulsations so as to adjust the time constants of said slow closing andslow releasing relays according to the speed of incoming pulsations.

WILLIAM WALTER MCGOFFIN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,287,396 Morse Dec. 10, 19181,597,763 Chauveau Aug. 31, 1926 1,655,689 Chauveau Jan. 10, 19281,930,631 Thompson Oct. 17, 1933 2,334,574 Neiswnter Nov. 16, 19432,334,575 Neiswnter Nov. 16, 1943 2,446,943 McGon Aug. 10, 1948 FOREIGNPATENTS Number Country Date 555,664 Great Britain Sept. 1, 1943

